Black, dark brown and dark olive drab paints of a spar-varnish type applied on the outside surface of ordinary window glass are recommended for blackouts, where it is necessary to paint windows such as skylights. The paint should be flat - not glossy - in order to avoid reflections. Application of blackout paint to the inside of glass causes a mirrorlike effect so that moonlight and flares are reflected more than by uncoated glass. An inside painting job on windows therefore, is not fully effective as a blackout. Light can be shut off and reflected glare eliminated by painting the outside of windows. To counteract the depressing effect of darkened windows, a white undercoat can be applied before the blackout paint. On plate glass, it is advisable to use lighter colored paint because dark colored paints absorb so much heat from the sun that the glassis likely to crack.